Eliot Roman a publié une note il y a 6 jours et 1 heure
Why some hosts become ill due to toxoplasmosis whereas most remain asymptomatic is largely unknown. The phenotypic and molecular characteristics of T. gondii are considered as factors in the pathogenesis of toxoplasmosis. Virulence of T. gondii has been traditionally assessed in outbred mice, and the strains are grouped as virulent if the inoculated mice die of toxoplasmosis, irrespective of the dose. In general, T. gondii strains from Brazil and Colombia are more mouse virulent than the rest of the world (Dubey et al., 2012; Cañón-Franco et al., 2014). However, currently there are no phenotypic characters of a T. gondii strain linking clinical disease in humans, although it dub ubiquitin has been speculated that higher clinical toxoplasmosis in South America is associated with unusual mouse virulent strains.Little is known of the mouse virulence of T .gondii strains from humans and animals in China. Chen et al. (2011) assessed virulence of 14 T. gondii isolates from cats into 10 SW mice by intraperitoneal inoculation with 1000 tachyzoites; nine strains killed all mice, three strains killed eight or nine of the 10 mice inoculated, whereas mice inoculated with one strain survived. However, it is not clear how tachyzoites were obtained or maintained. Qian et al. (2012) reported that strain TgCatBj2 was mildly pathogenic to BALB/c mice; six of 10 mice inoculated with 5000 tachyzoites died, whereas mice inoculated with 1000 tachyzoites survived.Wang et al. (2013b) tested pathogenicity of eight T. gondii strains from cats. Ten mice (strain not stated) were inoculated intraperitoneally with 1000 tachyzoites (number of passages in mice or cell culture not stated); mice inoculated with five strains died in three-eight days p.i., all mice inoculated with two strains survived, and one of 10 mice inoculated with one strain died.The route of inoculation and the strain of mouse are important determinants of pathogenicity; the inbred BALB/c mice are more resistant than SW mice and T. gondii is less pathogenic by the subcutaneous route versus the intraperitoneal route. Continued passages of a strain in mice or cell culture can alter the strain (Dubey, 2010). Therefore, it is important that these factors should be borne in mind before making conclusion concerning the virulence of strains. In the present study, all nine T. gondii strains were avirulent for SW mice. Thus, currently the existence of highly mouse virulent strains in China needs critical evaluation.Review of data in Table 2 indicates that the ToxoDB genotype #9 (Chinese 1) is the predominant genotype in cats in China. The genotype of T. gondii circulating in cats is epidemiologically important because humans become infected mostly by ingesting water or food contaminated with T. gondii oocysts or by eating undercooked meat of food animals that are in turn infected mostly via oocysts. Data concerning T. gondii genotypes in humans in China are limited with seven isolates so far (Zhou et al., 2009; Wang et al., 2013a,b). Genotyping of three isolates from humans by Zhou et al. (2009) revealed genotype #10 (1 strain) and #9 (2 strains). Wang et al. (2013a,b) isolated T. gondii tachyzoites of ToxoDB genotypes #9, #10, #1, and #204 from blood of four immunocompromized patients. There are no details concerning the other two human isolates. Thirteen isolates from pigs in China have been genotyped and reported in literature (Zhou et al., 2009; Wang et al., 2012a,b,c, 2013a; Li et al., 2015), revealing genotype #9 for 11 strains and #10 for two strains. In addition, genotype #3 (1 strain) was reported in a sheep (Zhou et al., 2009) and #225 (1 strain) in a chicken (Wang et al., 2013a). In our current study, ToxoDB genotype #1 (Type II) was isolated from feces of one cat, and genotype #2 (Type III) was also isolated from tissue of one cat. Both genotypes are wide spread worldwide (Shwab et al., 2014). Genotype #17 (also known as Type BrIV), which was previously reported in South America (Shwab et al., 2014), is now identified for the first time from a cat sample in China. Overall, our results showed the dominance of genotype #9 (6 strains), indicating limited genetic diversity of this parasite.